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Author Topic: 48vDC/300watt switching power supply and RFI noise?  (Read 3700 times)
AK4YA
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Posts: 106




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« on: August 22, 2012, 10:12:15 AM »

The link on ARRL says to find a PS with "low RFI" advertisements.  A linear on at this power is very expensive.  Can someone point me where I can educate myself on input and or output filters for switching power supplies to reduce RFI as much as possible?
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WB2WIK
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« Reply #1 on: August 22, 2012, 10:16:57 AM »

This model is a good one and has both line harmonic filtering and RFI output filtering, meeting CISPR 22(B) specifications.  It's not a toy:

http://www.trcelectronics.com/Cosel/pba300f-48.shtml

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AK4YA
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« Reply #2 on: August 22, 2012, 10:27:54 AM »

wow thats no toy for sure.  at that price I could get a linear one
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AC5UP
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Posts: 3822




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« Reply #3 on: August 22, 2012, 11:05:28 AM »

Think linear and this would not be a difficult homebrew project for someone practiced in the arts of scrounging...

As a general rule for linear supplies the lower the voltage the larger and more expensive the transformer for the same wattage.  The transformer is usually the difficult item for a project like this.  A 14 volt supply @ 21.5 Amps = 301 Watts while a 48 volt supply @ 6.25 amps = 300 Watts. Point being that a 7 to 8 amp transformer at 50 volts is far easier to find and work with than anything 20+ Amps at 14 volts.  It has been my experience that any multiple of 6 volts is not an oddball transformer... Like 12, 24, 36 or 48.

Look at it the right way and this could become an excellent learning opportunity.  It's true that I have been dragging swapmeet and surplus store junk home for decades so I don't see this as a difficult project, nor an expensive project, and you'll find plenty of schematics on the web.  Research a little further and you'll find that even the commercial guys have been known to parallel transformers to build current capability without custom iron. 

Your mileage may vary.
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N3QE
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« Reply #4 on: August 22, 2012, 11:11:19 AM »

Good grounding practices (AC power ground to PS frame; no other grounds connect to PS frame; deliver +/- DC wires to the load not relying on AC ground to be a power return return) and twisted wires for both AC input and DC output will help a lot in reducing RFI. One sure way to make a lot of RF hash is to have great big loops in the wires. That said, extra hash filters on AC in and DC out do not hurt any, preferably they go in the same metal box as the power supply module.

Some 300W class 48V switchers at reasonable prices below, I have used this class of products and RFI is not a problem with good wiring. First is open frame, second is closed frame:

http://www.digikey.com/product-detail/en/VF-S320-48A/102-1998-ND/2138650

http://www.digikey.com/product-detail/en/SWS30048/285-1621-ND/1631788

If you want a real nice enclosed box, the TDK/Lambda DIN rail mount supplies are super sweet. I buy these for work but they are too pricy for my personal use:

http://www.digikey.com/product-detail/en/DPP480-48-3/285-1936-ND/2170434
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WB2WIK
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« Reply #5 on: August 22, 2012, 11:17:12 AM »

wow thats no toy for sure.  at that price I could get a linear one

You probably could but if so, it wouldn't have the interesting qualities of a good SMPS.

For example, the SMPS can operate fine on any line voltage from 85 to 265V.  No switch or jumpers or mods required, just plug it into whatever you have.  It can also operate fine on line frequencies from 50 to 400 Hz.  This makes them very "universal" if you move around, visit foreign countries, etc.  Not so with most linear supplies.

SMPSs are also very light weight compared with linear.  Almost all decent quality SMPSs (industrial grade, such as the one I linked above) meet a huge number of compatibility specifications including voltage dips and interruptions.
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AK4YA
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Posts: 106




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« Reply #6 on: August 22, 2012, 11:31:22 AM »

Wow, I was just able to pick up a Acopian A50HT800 Linear Regulated 50V on ebay for 85+50 shipping.

AC5UP I really wish I could build it.  Im 100% sure I could given enough time.  I know this type of PS is one of the simpler things to do due to the large size of most of the components.
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WB2WIK
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« Reply #7 on: August 22, 2012, 11:43:36 AM »

Wow, I was just able to pick up a Acopian A50HT800 Linear Regulated 50V on ebay for 85+50 shipping.



Hope you get your $135 worth!  I see the item was sold from here in Los Angeles (Compton) and listed as "untested."

However it's also a "power seller" offering a return policy.  I hope it works okay, because the $50 to ship it back isn't covered by the seller warranty. Tongue

But I'd have high hopes.  Acopian makes good stuff and they've been around forever.
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AK4YA
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Posts: 106




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« Reply #8 on: August 22, 2012, 12:17:34 PM »

Wow, I was just able to pick up a Acopian A50HT800 Linear Regulated 50V on ebay for 85+50 shipping.



Hope you get your $135 worth!  I see the item was sold from here in Los Angeles (Compton) and listed as "untested."

However it's also a "power seller" offering a return policy.  I hope it works okay, because the $50 to ship it back isn't covered by the seller warranty. Tongue

But I'd have high hopes.  Acopian makes good stuff and they've been around forever.

Even if it doesnt work, possibly I could fix it as well.  Any idea how I can go about getting some sort of 6.25ohm 400watt resistive load to test it?  I dont really want to "test" it on my expensive new amp.
« Last Edit: August 22, 2012, 01:05:07 PM by KC5VNN » Logged
W9GB
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Posts: 2597




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« Reply #9 on: August 22, 2012, 12:47:50 PM »

Acopian A50HT800  --  Linear Regulated Power Supply
Acopian Gold Series -- 50 VDC at 8 Amps (at 40 C), their Series A.
$ 565.00 USD <new>

Terminal Strip Cover: Clips on. To order, add suffix "M" to model number and $5.00 to price.
Mounting kits:  
http://www.acopian.com/single-l-goldbox-a.html
==
Series A : High Performance (model numbers begin with the letter A)

A broad selection of power supplies offering unusually high performance - many models have regulation of ±0.005%. Electronic current limiting and provision for remote voltage sensing are standard features; overvoltage protection is available as a built-in option. Rugged extruded aluminum cases include threaded mounting holes on bottom, back, and side, permitting mounting in any position.

Provision for remote sensing and/or external output adjustment.
Short circuit proof with automatic recovery (electronic current limiting).

This would power an HF amplifier module up to 200 to 250 Watts RF.
http://www.acopian.com/single-l-goldbox-m.html

Instruction Sheet for Gold Box Series "A" Power Supplies
The second page has schematic diagram.
http://www.acopian.com/inc/streamFile.asp?loc=info&id=AcopianGoldBoxSeriesA.pdf

Acopian Technical Company
Easton, PA 18044. USA
Phone: +1 (610)-258-5441
http://www.acopian.com/default.asp

50-Volt power supplies
http://www.acopian.com/power-supply-voltages/50-volt-power-supplies.htm

« Last Edit: August 22, 2012, 01:17:29 PM by W9GB » Logged
AC5UP
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Posts: 3822




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« Reply #10 on: August 22, 2012, 01:39:47 PM »

Instruction Sheet for "A" Series Power Supplies
The second page has schematic diagram.
http://www.acopian.com/inc/streamFile.asp?loc=info&id=AcopianGoldBoxSeriesA.pdf

Note to KC5VNN:
The link shown above does have a schematic on the second page which is conveniently devoid of any part numbers or part values.  This is because Acopian uses essentially the same circuit on all their linear supplies and the part details will vary depending on the voltage range of the regulator board.  You'll find the supply series number penciled on the edge of the board which should match the model number.  Think of the regulator board as an LM-723 type design built from discrete parts (even though it isn't exactly the same circuit) with foldback on overcurrent and remote sensing capabilities.  I know this because two weeks ago I refurbed a pair of 1983 vintage 12 volt rack mount jobbies and there is nothing made from unobtanium or beyond your comprehension inside an Acopian power supply.

They are well made, have more pass transistors than they need, and are easy to work on. If yours does need repair I can tell you that mine have twin electrolytics in the ripple filter and I found no issues other than one weak cap.  Both were a no brainer to diagnose and needed a mod to bump the voltage adjustment range upward.  A 100 Ohm resistor in series with the trimpot gave me a max of 13.725 volts out and that's close enough to 13.8 VDC for what I do.

BTW: When the supply comes in, take a look at the pass transistors. If they're like mine you'll see a cryptic part number, RCA logo, then another number like " 8346 ". That tells me the transistors were made during the 46th week of 1983 so assuming normal delay times my supplies came off the line at Acopian in late '83 or early '84.

29 years later they're both voltworthy.
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WB2WIK
Member

Posts: 20542




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« Reply #11 on: August 22, 2012, 01:43:13 PM »

Wow, I was just able to pick up a Acopian A50HT800 Linear Regulated 50V on ebay for 85+50 shipping.



Hope you get your $135 worth!  I see the item was sold from here in Los Angeles (Compton) and listed as "untested."

However it's also a "power seller" offering a return policy.  I hope it works okay, because the $50 to ship it back isn't covered by the seller warranty. Tongue

But I'd have high hopes.  Acopian makes good stuff and they've been around forever.

Even if it doesnt work, possibly I could fix it as well.  Any idea how I can go about getting some sort of 6.25ohm 400watt resistive load to test it?  I dont really want to "test" it on my expensive new amp.

That's an expensive resistor.  However four 12V automotive headlamps wired in series could be a fairly cheap load that should draw about 200W.  Double that up with another string in parallel with the first and it should draw about 400W.  Headlamps are pretty inexpensive.

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K5LXP
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Posts: 4448


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« Reply #12 on: August 22, 2012, 03:19:41 PM »

Any idea how I can go about getting some sort of 6.25ohm 400watt resistive load to test it?  I dont really want to "test" it on my expensive new amp.

Steel wire works well as a DC dummy load.  I've built loads that will put the hurt to 20A supplies to 150A battery loads.  Steel picture hanging wire is good for low currents, and fence wire is good for larger loads.  For tests more than a few seconds coil the wire up and put it in a bucket of water, otherwise it will get hot and change resistance.  Way cheaper and easier to manage than banks of light bulbs. Add a shunt and a DVM and you're good to go.

Mark K5LXP
Albuquerque, NM
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KE4DRN
Member

Posts: 3714




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« Reply #13 on: August 22, 2012, 04:55:13 PM »

hi,

Lambda also made great power supplies and they show up
all the time on ebay, often they sell for a lot less then
what they went for new.  look for alpha or vega series,
400 to 600 and even 1,000W switching mode supplies,
easy to adjust output voltages. 
You can combine the modules if you want and experiment.

I like using the headlight load, local car recycle yard has
lots of them very inexpensive.

73 james
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AK4YA
Member

Posts: 106




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« Reply #14 on: August 23, 2012, 08:34:28 AM »

That's an expensive resistor.  However four 12V automotive headlamps wired in series could be a fairly cheap load that should draw about 200W.  Double that up with another string in parallel with the first and it should draw about 400W.  Headlamps are pretty inexpensive.

I can get two 24V/250watt overhead projector bulbs for $4 on amazon. If these specs expect an AC source, could I expect the DC resistance here to be too much different than the AC impedance at 60hz?
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